Flash-proof rim mold and method of making

Abstract

A flash-proof RIM mold and method of making same. The mold has a thermosetting resin squeezed and cured between the mold portions at the edge of the parting line exposed to the mold cavity. The resin fills any gaps between the mold portions resulting from mismatched surfaces. The resin adheres to one mold portion and is readily spaceable from the other. A strip of uncured resin is applied to one of the mold portions, the mold closed at its operating temperature, and the resin allowed to cure to a semi-cured state. The mold is opened and any resin exuding into the mold cavity removed. After the resin has fully cured the mold is ready for use.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a metal, reaction-injection-molding mold comprising first and second mating segments which, in a mold-closed position, define a cavity therebetween for receiving a liquid mixture of reactants and said first and second segments each have complimentary shaped faces which mate one with the other at a parting line having an edge exposed to said cavity, the improvement comprising an interlayer of thermosetting resin between said faces contiguous said edge and filling any gaps between said faces at said:edge so as to prevent intrusion of said parting line by said reactants and the coincident formation of flash on articles formed in said cavity, wherein said resin (a) adheres firmly to one of said faces, (b) is readily separable from the other of said faces and (c) is cured in situ between said faces when said mold is in said mold-closed position so as to provide an exposed surface thereon in the mold-open position which conforms to the topography of said other of said faces. 
     
     
       2. The mold according to claim 1 wherein said resin comprises an epoxy resin. 
     
     
       3. The mold according to claim 2 wherein said epoxy contains a particulate filler selected from the group consisting of ceramics and metals. 
     
     
       4. A method of making a substantially flash-proof metal, reaction-injection-molding mold comprising first and second mating portions defining a molding cavity for receiving a liquid mixture of reactants, said first and second portions each having complimentary shaped faces which mate one with the other at a parting line having an edge exposed to said cavity, comprising the steps of: preparing a first surface of one of said faces adjacent said edge to receive and adherently retain a film of thermosetting resin applied thereto;   preparing a second surface of the other of said faces adjacent said edge to prevent adherence of said thermosetting resin thereto;   heating the mold portions to a temperature near the temperature at which said mold normally operates;   applying a strip of thermosetting resin to one of said surfaces;   closing said mold so as to mate said portions one to the other, and cause said resin to flow and distribute itself between said surfaces so as to fill any gaps therebetween;   while said mold is closed, curing said resin to a semi-cured state which is sufficiently hard that the resin will retain any contours formed therein by the closed mold;   opening said mold such that said resin adheres to said first surface and separates from said second surface;   trimming off any semi-cured resin that might have exuded from said edge into said cavity; and   allowing said resin to completely cure; whereby a mold is formed having a parting line which resists intrusion by said liquid reactants at said edge.     
     
     
       5. A method according to claim 4 wherein said thermosetting resin is an epoxy. 
     
     
       6. A method according to claim 4 wherein said preparing includes roughening said first surface to provide a plurality of sites for anchoring said resin to said surface. 
     
     
       7. A method according to claim 4 including the step of coating said second surface with a release agent. 
     
     
       8. A method according to claim 7 wherein said release agent is selected from the group consisting of soap and wax. 
     
     
       9. A method according to claim 4 wherein said resin has a curing temperature near said operating temperature and said resin is applied to said surface before said mold portions are heated to said operating temperature. 
     
     
       10. A method according to claim 4 wherein said resin is applied to said surface after said mold portion has been heated to said operating temperature and just before said mold is closed. 
     
     
       11. A method according to claim 4 wherein said strip varies in width from about 0.015 inches to about 0.500 inches. 
     
     
       12. The mold according to claim 1 wherein said resin is selected from the group consisting of epoxies, silicones, polyesters and polyurethanes.